Recent reductions in age requirements for cochlear implantation (currently FDA-approved at 12 months) have made it possible for deaf infants and toddlers to begin to hear at ages when many foundational speech skills are normally acquired. Thus, receiving a cochlear implant (Cl) at a young age may lead to a more typical trajectories for speech development and, ultimately, closer to normal levels of speech intelligibility than observed for children implanted at older ages. To date, however, very little is known about how very young Cl recipients become talkers. The principal objective of this revised research proposal is to obtain a better understanding of the effects of Cl experience on speech development in children implanted by their third birthdays. The specific aims of the study will be met by analyzing the emergence of key speech behaviors such as intonation control, vocal development, phonetic expansion, and spoken vocabulary. Phonological abilities at 2 years post-implant activation will also be measured. Data from children with CIs will be compared to that of infants and toddlers who have normal hearing so that the efficiency of post- implantation speech learning can be assessed. In addition, the effects of age-at-implantation on speech development will also be examined. Current clinical practices for infants and toddlers-both the implant decision-making process and communication intervention planning-are not guided by research regarding the effects of implantation on early speech development. The findings of this project will help to inform the cochlear implant decision making process regarding an optimal age-range for implantation, will provide empirical data for assessing the adequacy of post-implantation speech learning, and will be useful in selecting developmentally appropriate intervention goals for young Cl recipients. The objectives of this study will be met through between group comparisons (e.g., NH vs. Cl groups, and younger vs. older age-at-implantation groups) and through a prospective longitudinal design that includes parent-child interactions, parent reports, and elicited speech samples. This investigation examines speech development in deaf children who receive cochlear implants before their third birthdays. Comparisons with typically developing toddlers and among children implanted at different ages are undertaken through a prospective longitudinal research design.